1. Field of the Invention
Aspects of the present invention relate to an image forming apparatus and a control method thereof, and more particularly, to an image forming apparatus which controls an image forming characteristic using a test image and a control method thereof.
2. Description of the Related Art
An image forming apparatus, such as a laser printer, a copier, and a multi-function device, controls an exposure of a photosensitive member to develop toner, and then transfers and fuses the toner on a printing medium to thereby form an image. In general, an image forming apparatus which can form a color image includes an image forming unit having a laser scanning unit (LSU), a plurality of photosensitive members, a plurality of transfer rollers, etc., which are provided in correspondence to a plurality of colors. For example, a plurality of photosensitive members is arranged along a transport path of a printing medium. The printing medium is transferred along the transport path by a transport unit such as a transport belt.
To control an image forming characteristic of an image forming unit, such as a developing condition and a color registration, the image forming apparatus forms an image (hereinafter, referred to as a “test image”) to test qualities of the image forming apparatus in order to determine the image forming characteristic.
FIG. 1 illustrates the formation of a test image by a conventional image forming apparatus. A reference numeral 1 denotes a transport belt. A reference numeral 2 denotes a test image formed in correspondence to plural colors (hereinafter, the test image may also be referred to as a “density mark”).
A conventional image forming apparatus transfers toner at a predetermined position on the surface of a transport belt 1 according to test data which is provided to control an image formation characteristic. The transferred toner forms a density mark 2. The image forming apparatus forms the density mark 2 while moving the transport belt 1 in the same way that the transport belt 1 is moved during an actual printing operation, except that the density mark 2 is formed on the transport belt 1 instead of a printing medium. In FIG. 1, a reference character “A” denotes a transporting direction of the transport belt 1.
As illustrated in FIG. 1, the image forming apparatus forms four density marks 2 in correspondence to each color of C (Cyan), M (Magenta), Y (Yellow) and K (Black). Each density mark 2 has a substantially rectangular shape.
The image forming apparatus includes a detector 3 which detects the density mark 2. The detector 3 irradiates light at a predetermined driving voltage and detects light reflected from the density mark 2. The image forming apparatus evaluates the density of the density mark 2 using a detection result obtained by the detector 3. The image forming apparatus determines an image forming characteristic, for example, a developing condition or a color registration condition, based on the calculated density of the evaluated density mark 2.
The detector 3 can perform detection of one density mark 2 multiple times in order to obtain a highly reliable detection result. In addition, instead of only using one detector 3 to detect the density of the density mark, a plurality of detectors 3 can be disposed across a transporting direction “A” of the transport belt 2, to thus perform detection sequentially. In this case, a size “W” of the density mark 2 of each color can be determined by using the following equation (1):W(mm)=[Transporting speed of transport belt(mm/s)]×[Detection time (sec)]×[The number of times of detection]×[The number of detectors]  (Equation (1)).
In Equation 1, the transporting speed of the transport belt refers to the speed at which the transport belt 1 moves the density mark past the detector 3, the detection time refers to time taken by the detector 3 to perform a detection operation one time, the number of times of detection refers to the number of times which the detector 3 performs a detection operation to analyze the density mark, and the number of detectors refers to the number of detectors 3 used during the detection operation.
In addition, the conventional image forming apparatus can control an image forming characteristic repeatedly while changing a drive voltage level of the detector 3 to get a more reliable detection result. In this case, as illustrated in FIG. 1, plural density marks 2 need to be formed on the transport belt 1.
As such, when an image formation characteristic is controlled using a test image, an amount of toner consumed to form the test image depends on the characteristic of the image forming apparatus. That is, when the transporting speed of the transport belt 1 is fast, and when a detection mark is to be analyzed in a highly reliable fashion, the detector 3 or plurality of detectors 3 require a large amount of toner to have sufficient time to analyze the passing density mark, thereby causing a problem of toner consumption.
Also, since the toner transferred to the transport belt 1 to form a test image becomes waste toner, an amount of the waste toner becomes large. Even if the toner transferred to the transport belt 1 is recollected using a reverse transferring method, there is a problem in that a reverse transferring time is prolonged.